We have a generator like this: http://www.hondapowerequipment.com/eu1000.htm which we use to provide us with 240V and 12V feeds in a mobile environment. Unfortunately, as soon as we turn it on it causes us to lose radio reception in another piece of equipment. This other equipment (let’s call it box ‘B’) is used to pick up radio signals in the 300KHz range.
I have tried to stop this happening by shortening the antenna cable to box B, separating the generator and box B as much as possible, and by placing the generator in a home-made faraday cage, all to no avail. The generator seems to cause no problem with other radio equipment, possibly due to the different frequencies they operate on, possibly due to the comparative weakness of the 300KHz signal.
Does anyone know a simple and effective way to suppress the interference from the generator? Is there a simple suppressor I can fit, and if so… what? how? where? Would shielding on the box B antenna cable help? It is simple coax cable.
Many thanks in advance for any ideas you can give me.
Is box B powered from the generator? If so then the interference might be travelling down the power line which would explain why all of your attempts to filter it from the air would not work very well. You could put a 300 kHz notch filter on the power line, though I’m not sure where you could buy one commercially. It would be easy enough to construct for anyone with a bit of electronics knowledge.
Good question, sorry I didn’t mention this. Indeed box B was initially powered from the generator, but the first thing I did to try to elimintae the interference was disconnect it and connect it to an independent battery pack.
You could try placing a few snap-on ferrite chokes to the power line leading from the generator. Place them right at the point where the wire connects to the generator. You may need more than one. Depending on how long it is, the power line may act as an effective antenna, and these ferrite chokes should prevent that.
Grounding the chassis of the generator may also help. Drive an 8-foot grounding rod into the ground near the generator and run a heavy grounding strap from the metal frame of the generator to the rod. This will ground out an EMI that’s radiating from the generator chassis itself.
I had considered this, and I have some ferrite chokes I can use. However, I believe (and I have not been doing these tests myself, I need to confirm this with a colleague), that the interference effect is the same even when no appliance is connected to the generator. By this I mean that there is not even a power lead connected.
This is an excellent suggestion, but there are problems. The first is that the generator is almost entirely encased in a plastic housing (what isn’t these days?) and finding a connection point could be a problem. The second issue is that we regularly use this in a marine environment. Would ‘earthing’ to the water be effective, or for that matter, advisable?
My rather ill-educated guess is that the source of the interference is inherent in the generator itself, sparking from the brushes? Presumably this EMI is picked up by the antenna cable to Box B. Does this make sense, and is there anything I can do about it?
A capacitor of the correct voltage and capacitance should solve you problem.
Just connect across generator output. Sorry I can’t furnish cap size but voltage 2x or more the output voltage of generator. Might try two or tree different valuse to find best suppression.
Does the noise get worse if you change the load on the 12 V. dc output? You might try putting a varistor, say 15 V or so limiting voltage, on the dc output.
You AC generator might not have any brushes. It’s probably like an automobile alternator only single phase instead of three phase. These consist of a stator with the output windings and a permanent magnet rotor and they are brushless.
It could also be ignition noise from the motor, although that’s not so likely with electronic ignition.
On thinking it over the dc output is probably also brushless so a varistor wouldn’t help. I suspect the generator has a low voltage winding which is rectified to produce the dc output.
I have been experimenting today, and I have found the following:
i) The shorter the antenna cable on box B, the less the effect of the interference.
ii) Ferrites seem to have no discernible effect.
iii) The generator has a Ground terminal screw, but the manual gives no guidance on how, when or whether it should be connected. It is limited to suggesting I ‘consult a qualified electrical engineer’.
iv) This model of generator has an alternator built in to the engine itself. The output is from a micro-processor controlled inverter.
I am thinking of connecting a wire to the grounding point and experimenting, does anyone think this is a dangerous, foolish idea?
It’s not likely dangerous, per se, however you’ll want to be aware that this may (depending on what this ground terminal is connected to internally.) tie the neutral to ground, which would make your system ground-referenced. This is not bad in and of itself, since your house wiring is no different. However, it exposes you to a potential shock hazard that a non-ground-referenced doesn’t possess, so you’ll want to use the same degree of caution you would with residential wiring. It may also just ground the frame and chassis of the generator. You can test this with an ohmmeter connected between the neutral and the ground terminal. If you get close to zero ohms, then the caveat above applies. If not, I can’t see any possible harm.
I am very grateful to you… I believe the manual says that the Neutral is NOT connected to the grounding point. I shall check this out.
At the risk of prolonging the life of a tired and seemingly uninteresting thread, can I ask if anyone can comment on the practicability and probable effectiveness of grounding such a piece of equipment to water in a marine environment?
I agree. With a generator you have the luxery of isolating the 120/240 AC from earth ground. This is a safer situation when compared to your home wiring, which is earth ground referenced.
I’m really rusty at this stuff, but could there be a relationship (harmonics?) between the 60hz power and the 300khz signal? The OP mentions antenna length being a factor.
Peace,
mangeorge
I can’t speak from experience here, but aside from the eek! response that people have when water and electricity mix, I can’t think of any reason it wouldn’t make for a reasonably effective signal ground. I would not recommend this as a safety ground, however, since you want a really good, reliable connection to Earth for that, something which I’m not convinced you’d necessarily have through saltwater. In this case, I’d say you certainly want to be sure there is NO connection to the neutral line whatsoever, and that you’re only grounding the generator chassis. Before you proceed, however, I’d like to see a response from someone with some practical grounding experience in a marine environment.
Mangeorge, It’s more likely to be broadband noise being produced, either by brushes in the generator, the motor ignition system of some similar souce. I doubt if harmonics have anything to do with this situation. A 300 kHz notch filter on the antenna input of the affected device may do the trick.
In case of a boat a safety ground would be to the structure of the boat if the boat is metal. Then the hot and neutral ac and dc wiring would be isolated from the hull except that the neutrals would be connected to the safety ground at one point, just like on the land, which could be the grounding terminal on the generator.
I downloaded the circuit diagram. What you have is an ordinary three-phase alternator with several auxilliary output windings and it is probably brushless so sparking of the brushes isn’t the problem. I suspect they go to the trouble of rectifying the alternator output and using an inverter because the frequency control with changing loads wouldn’t be too good if they depended on motor speed control. From the blurb in your cite it seems that the ac output is a pretty good looking sine wave. It is probably better than that of the power in a house and I suspect that isn’t the cause of the noise.
From the circuit diagram it looks to me like the noise source is the motor ignition system. Try connecting the Ground Terminal to the chassis of the radio that’s having problems. On the circuit diagram there is a terminal labeled “Frame Ground” and one labeled “Ground Terminal” and it appears that they are connected together so if both terminals appear on your generator they are the same electrically and you can use either one.
To post a follow up in case anyone uses this thread for a similar problem.
Many thanks to all those who have contributed. So far, no luck though. I have tried grounding the generator chassis to the radio box chassis and grounding the generator to the water, both to no avail. So far I am stumped, I still cannot operate Box B while the generator is running. All other radios I have tried, for example marine band VHF, do not seem to be affected.
One solution, although it might not be cheap or simple, is to shield the ignition system. I’ve seen this done in military equipment where RFI (radio frequency interference) was a concern. All of the ignition cables had braided metal shields and components like the distributer were enclosed in metal cans.